Many conventional electronic ballast circuits provide lamp power signals that cause lamp striations during the operation of the gas-discharge lamp. Lamp striations are zones of light intensity that appear as dark bands and may cause the lamp to operate with an undesirable strobing effect.
There are two known ways of reducing lamp striations. The first is to perform lamp current amplitude modulation. The disadvantage of this technique is that it requires complex and costly electronic circuits. The other method is to create an asymmetrical lamp power signal by superimposing a DC component signal onto the lamp power signal. Prior art ballast circuits accomplish this by manipulating inverter switch devices in the ballast circuit. For example, the inverter switch devices in the ballast circuit may be switched at asymmetrical switch frequencies. While this technique is effective in creating an asymmetrical lamp power signal, operating the inverter switch devices at asymmetrical switch frequencies may cause unnecessary harmonic distortion in the ballast circuit.
What is needed is a ballast circuit that reduces lamp striations in a more efficient manner without utilizing complicated electronic circuits that increase the cost of the ballast.